When hydrogen gas to be used as fuel to a hydrogen vehicle is subjected to adiabatic expansion at a high pressure (isenthalpic expansion) in an expansion valve installed in a hydrogen gas filling line, the temperature of the hydrogen gas after the expansion rises by nature according to the Joule-Thomson effect because the expansion occurs at temperatures higher than the inversion temperature (−58° C.) owing to its nature. Therefore, when hydrogen gas as fuel to hydrogen vehicles is filled from a hydrogen gas supply source at a hydrogen station into a fuel tank of a hydrogen vehicle, the hydrogen gas temperature is increased in an expansion valve installed in the hydrogen gas filling line.
The higher the expansion ratio of hydrogen gas, the more the hydrogen gas temperature rise becomes noticeable. Therefore, if the supply gas pressure from the hydrogen gas supply source at a hydrogen station (supply source tank pressure) is increased, for example, if it is increased from 45 to 70 MPa (G), or further to 82 MPa (G), its own temperature rise increases accordingly.
When the hydrogen gas from a supply source tank at a pressure 70 MPa (G), and 30° C., is expanded in one step, the gas temperature changes at the secondary pressure, as the respective changes are shown by way of example in FIG. 1.
In addition, when hydrogen gas is filled at a differential pressure into a closed space such as an onboard fuel tank of a vehicle, the temperature of the filled hydrogen gas in the fuel tank further rises on account of the compression of the gas at the time of the filling.
On the other hand, for a currently prevailing fuel cell vehicle, the highest temperature limit at hydrogen filling is set at 85° C. in consideration of the temperature limitation by fuel tank material as well as of temperature limitation by the operation of a fuel cell.
If hydrogen gas should be filled without any temperature control means, the temperature of the hydrogen gas at gas filling will rise above the highest temperature limit of 85° C., to cause the problems of temperature limitation by fuel tank material, temperature limitation by the operation of a fuel cell, and pressure drop due to cooling after filling, because of the nature of hydrogen as described above. In order to prevent such problems, a process of installing a cooling means, such as a thermocouple, in a hydrogen gas filling line and filling hydrogen gas in a hydrogen vehicle while cooling the hydrogen gas by means of the cooling means has been proposed and commercialized (see, e.g., Patent Document 1).